The tension in a string is uniform

Not always.

Some conditions are necessary to tension be constant:

1. String is mass-less.

2. String is inextensible.

3. There is no friction between string and pulley.

4. For string with mass, if it is fixed, then tension will be uniform.

In your case, option 3 has been violated (there is friction between pulley and string).

The tension in a string is uniform

Not always.

The tension of the string is uniform in some cases:

1. If String is mass-less and its particles don't move with respect to each other (i.e. string is inextensible or if it is extensible, it reach to its final tension).

2. If String is mass-less and there is no friction between string and pulley.

3. For string with mass, if it is fixed, then tension will be uniform.

In your case, option 2 has been violated (there is friction between pulley and string).

tension the tension in a string is uniform

Not always.

Some conditions are necessary to tension be constant:

1. String is mass-less.

2. String is inextensible.

3. There is no friction between string and pulley.

4. For string with mass, if it is fixed, then tension will be uniform.

In your case, option 3 has been violated.

The tension in a string is uniform

Not always.

Some conditions are necessary to tension be constant:

1. String is mass-less.

2. String is inextensible.

3. There is no friction between string and pulley.

4. For string with mass, if it is fixed, then tension will be uniform.

In your case, option 3 has been violated (there is friction between pulley and string).